Could X-ray afterglows be standard candles?

Standard candle

Astrobods love standard candles. Love ’em. And it ain’t hard to understand why.

When ya look out into the darkness, it’s easy to see where everything fits into the celestial sphere. It ain’t quite so simple to see in which layer it sits in the celestial onion. So astronomers look for standard candles, objects whose distance they can measure by some other means.

One of the most famous and useful standard candles are Type Ia supernovas which have a known luminosity. So the brighter they look to us, the nearer they must be (which ain’t true for ordinary stars cos brighter stars might just be big ones a long way off). In fact, astronomers can work out the distance of Type Ia supernovas pretty accurately by measuring the apparent brightness here on Earth (assuming there ain’t no dust in the way).

The trouble is that we can only see Type Ia supernovas in our own galaxy and a few of the nearest others. That leaves a few hundred million galaxies whose distance is almost impossible to measure accurately.

Now Bruce “Which” Gendre at the Istituto di Astrofisica Spaziale e Fisica Cosmica in Rome and buddies reckon they’ve found another standard candle in the form of the X-ray afterglow that follows gamma ray bursts. The sources seem to have a standard luminosity so measuring the amount of light that reaches Earth gives you a good idea how far off they are.

Which Gendre and his pals have even tested the idea against another way of measuring distance from the redshift of the light (technically that just tells you have fast the source is moving away from you, not its distance but alotta bods assume that more redshift = further away.) Bruce reckon his new method is pretty much in agreement with redshift data.

Obviously this is an idea that’ll need a little more testing but it could be a refreshing new way to determine distances over cosmological scales. And that’s gonna get them astrobods excited, bless ’em.

Ref: arxiv.org/abs/0711.2222: X-ray Afterglow Light Curves: towards a standard candle?

2 Responses to “Could X-ray afterglows be standard candles?”

  1. Miguel V. says:

    Good news, but few mistakes in the article. The supernovae which are standard candles are the type Ia. White dwarfs that reach a certain mass threshold. As all of them have the same mass, they are very homogeneous.

    However the most famous standard candles are cepheids stars (bright variable stars), which allowed Hubble to deduce the expansion of the universe and calibrate SNe Ia as standard candles, among other indicators

  2. KFC says:

    Thanks man, that’s changed